Method and device for electromagnetic cooking

ABSTRACT

An electromagnetic cooking device includes an enclosed cavity; a set of radio frequency feeds configured to introduce electromagnetic radiation into the enclosed cavity to heat up and prepare food; a set of high-power radio frequency amplifiers coupled to the set of radio frequency feeds, each high-power amplifier comprising at least one amplifying stage configured to output a signal that is amplified in power with respect to an input radio frequency signal; a signal generator coupled to the set of high-power radio frequency amplifiers for generating the input radio frequency signal, and a controller. The controller can be configured to, among other things, cause the signal generator and selected ones of the set of high-power amplifiers to output a radio frequency signal, select from a set of phase values of radio frequency electromagnetic waves, and identify the resonant modes excited within the enclosed cavity.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority to U.S. ProvisionalPatent Application No. 62/170,416, filed on Jun. 3, 2015, the disclosureof which is incorporated herein by reference in its entirety.

BACKGROUND

The present device generally relates to a method and device forelectromagnetic cooking, and more specifically, to a method and devicefor determining and controlling the resonant modes within a microwaveoven.

A conventional microwave oven cooks food by a process of dielectricheating in which a high-frequency alternating electromagnetic field isdistributed throughout an enclosed cavity. A sub-band of the radiofrequency spectrum, microwave frequencies at or around 2.45 GHz causedielectric heating primarily by absorption of energy in water.

To generate microwave frequency radiation in a conventional microwave, avoltage applied to a high-voltage transformer results in a high-voltagepower that is applied to a magnetron that generates microwave frequencyradiation. The microwaves are then transmitted to an enclosed cavitycontaining the food through a waveguide. Cooking food in an enclosedcavity with a single, non-coherent source like a magnetron can result innon-uniform heating of the food. To more evenly heat food, microwaveovens include, among other things, mechanical solutions such as amicrowave stirrer and a turntable for rotating the food. A commonmagnetron-based microwave source is not narrowband and not tunable (i.e.emits microwaves at a frequency that is changing over time and notselectable). As an alternative to such a common magnetron-basedmicrowave source, solid-state sources can be included in microwave ovenswhich are tunable and coherent.

SUMMARY

In one aspect, an electromagnetic cooking device includes an enclosedcavity; a set of radio frequency feeds configured to introduceelectromagnetic radiation into the enclosed cavity to heat up andprepare food; a set of high-power radio frequency amplifiers coupled tothe set of radio frequency feeds, each high-power amplifier comprisingat least one amplifying stage configured to output a signal that isamplified in power with respect to an input radio frequency signal, asignal generator coupled to the set of high-power radio frequencyamplifiers for generating the input radio frequency signal, and acontroller. The controller is configured to cause the signal generatorand selected ones of the set of high-power amplifiers to output a radiofrequency signal of a selected frequency, a selected phase value and aselected power level, wherein the selected frequency is selected from aset of frequencies in a bandwidth of radio frequency electromagneticwaves, the selected phase value is selected from a set of phase valuesof radio frequency electromagnetic waves, and the selected power levelis selected from a set of power levels and identify the resonant modesexcited within the enclosed cavity.

In another aspect, a method of exciting an enclosed cavity with radiofrequency radiation includes exciting the enclosed cavity with aselected set of phasors for a set of frequencies; collecting forward andreflected power measurements for the selected set of phasors;determining an efficiency spectrum for the selected set of phasors;identifying the resonant modes of the enclosed cavity based on thecomputed efficiency spectrum; and classifying foodstuff located withinthe enclosed cavity based on the identified resonant modes.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a block diagram of an electromagnetic cooking device withmultiple coherent radio frequency feeds in accordance with variousaspects described herein.

FIG. 2 is a block diagram of a radio frequency signal generator of FIG.1.

FIG. 3 is a schematic diagram illustrating a high-power radio frequencyamplifier coupled to a waveguide in accordance with various aspectsdescribed herein.

FIG. 4 is a cross-sectional diagram illustrating an integratedcirculator for use in a high-power radio frequency amplifier inaccordance with various aspects described herein.

FIG. 5 is a top-view diagram illustrating the integrated circulator ofFIG. 4.

FIG. 6 is a schematic diagram illustrating a high-power radio frequencyamplifier coupled to a waveguide with an integrated measurement systemin accordance with various aspects described herein.

FIG. 7 is a schematic diagram illustrating a high-power radio frequencyamplifier coupled to a waveguide with an integrated measurement systemincluding a reflectometer in accordance with various aspects describedherein.

FIG. 8 is a schematic diagram illustrating a resonant cavity coupled totwo radio frequency waveguides in accordance with various aspectsdescribed herein.

FIG. 9 is a graphical diagram illustrating efficiency versus frequencyfor in-phase and antiphase excitations of the resonant cavity of FIG. 8.

FIG. 10 is a diagram illustrating features of a method of analysis todetermine the resonant modes of the cavity in accordance with variousaspects described herein.

FIG. 11 is a diagram illustrating features of a method to characterizethe resonant modes of the cavity in accordance with various aspectsdescribed herein.

FIG. 12 is a schematic diagram illustrating features of a method tolocate and classify foodstuff positioned within a resonant cavity inaccordance with various aspects described herein.

FIG. 13 is a flowchart illustrating a method of identifying resonantmodes and classifying foodstuff positioned within a resonant cavity inaccordance with various aspects described herein.

DETAILED DESCRIPTION

It is to be understood that the specific devices and processesillustrated in the attached drawings, and described in the followingspecification are simply exemplary embodiments of the inventive conceptsdefined in the appended claims. Hence, other physical characteristicsrelating to the embodiments disclosed herein are not to be considered aslimiting, unless the claims expressly state otherwise.

A solid-state radio frequency (RF) cooking appliance heats up andprepares food by introducing electromagnetic radiation into an enclosedcavity. Multiple RF feeds at different locations in the enclosed cavityproduce dynamic electromagnetic wave patterns as they radiate. Tocontrol and shape of the wave patterns in the enclosed cavity, themultiple RF feeds can radiate waves with separately controlledelectromagnetic characteristics to maintain coherence (that is, astationary interference pattern) within the enclosed cavity. Forexample, each RF feed can transmit a different frequency, phase and/oramplitude with respect to the other feeds. Other electromagneticcharacteristics can be common among the RF feeds. For example, each RFfeed can transmit at a common but variable frequency. Although thefollowing embodiments are directed to a cooking appliance where RF feedsdirect electromagnetic radiation to heat an object in an enclosedcavity, it will be understood that the methods described herein and theinventive concepts derived herefrom are not so limited. The coveredconcepts and methods are applicable to any RF device whereelectromagnetic radiation is directed to an enclosed cavity to act on anobject inside the cavity. Exemplary devices include ovens, dryers,steamers, and the like.

FIG. 1 shows a block diagram of an electromagnetic cooking device 10with multiple coherent RF feeds 26A-D according to one embodiment. Asshown in FIG. 1, the electromagnetic cooking device 10 includes a powersupply 12, a controller 14, an RF signal generator 16, a human-machineinterface 28 and multiple high-power RF amplifiers 18A-D coupled to themultiple RF feeds 26A-D. The multiple RF feeds 26A-D each couple RFpower from one of the multiple high-power RF amplifiers 18A-D into anenclosed cavity 20.

The power supply 12 provides electrical power derived from mainselectricity to the controller 14, the RF signal generator 16, thehuman-machine interface 28 and the multiple high-power RF amplifiers18A-D. The power supply 12 converts the mains electricity to therequired power level of each of the devices it powers. The power supply12 can deliver a variable output voltage level. For example, the powersupply 12 can output a voltage level selectively controlled in 0.5-Voltsteps. In this way, the power supply 12 can be configured to typicallysupply 28 Volts direct current to each of the high-power RF amplifiers18A-D, but can supply a lower voltage, such as 15 Volts direct current,to decrease an RF output power level by a desired level.

A controller 14 can be included in the electromagnetic cooking device10, which can be operably coupled with various components of theelectromagnetic cooking device 10 to implement a cooking cycle. Thecontroller 14 can also be operably coupled with a control panel orhuman-machine interface 28 for receiving user-selected inputs andcommunicating information to a user. The human-machine interface 28 caninclude operational controls such as dials, lights, switches, touchscreen elements, and displays enabling a user to input commands, such asa cooking cycle, to the controller 14 and receive information. The userinterface 28 can include one or more elements, which can be centralizedor dispersed relative to each other. The controller 14 may also selectthe voltage level supplied by power supply 12.

The controller 14 can be provided with a memory and a central processingunit (CPU), and can be preferably embodied in a microcontroller. Thememory can be used for storing control software that can be executed bythe CPU in completing a cooking cycle. For example, the memory can storeone or more pre-programmed cooking cycles that can be selected by a userand completed by the electromagnetic cooking device 10. The controller14 can also receive input from one or more sensors. Non-limitingexamples of sensors that can be communicably coupled with the controller14 include peak level detectors known in the art of RF engineering formeasuring RF power levels and temperature sensors for measuring thetemperature of the enclosed cavity or one or more of the high-poweramplifiers 18A-D.

Based on the user input provided by the human-machine interface 28 anddata including the forward and backward (or reflected) power magnitudescoming from the multiple high-power amplifiers 18A-D (represented inFIG. 1 by the path from each of the high-power amplifiers 18A-D throughthe RF signal generator 16 to the controller 14), the controller 14 candetermine the cooking strategy and calculate the settings for the RFsignal generator 16. In this way, one of the main functions of thecontroller 14 is to actuate the electromagnetic cooking device 10 toinstantiate the cooking cycle as initiated by the user. The RF signalgenerator 16 as described below then can generate multiple RF waveforms,that is, one for each high-power amplifier 18A-D based on the settingsindicated by the controller 14.

The high-power amplifiers 18A-D, each coupled to one of the RF feeds26A-D, each output a high power RF signal based on a low power RF signalprovided by the RF signal generator 16. The low power RF signal input toeach of the high-power amplifiers 18A-D can be amplified by transformingthe direct current electrical power provided by the power supply 12 intoa high power radio frequency signal. In one non-limiting example, eachhigh-power amplifier 18A-D can be configured to output an RF signalranging from 50 to 250 Watts. The maximum output wattage for eachhigh-power amplifier can be more or less than 250 Watts depending uponthe implementation. Each high-power amplifier 18A-D can include a dummyload to absorb excessive RF reflections.

The multiple RF feeds 26A-D couple power from the multiple high-power RFamplifiers 18A-D to the enclosed cavity 20. The multiple RF feeds 26A-Dcan be coupled to the enclosed cavity 20 in spatially separated butfixed physical locations. The multiple RF feeds 26A-D can be implementedvia waveguide structures designed for low power loss propagation of RFsignals. In one non-limiting example, metallic, rectangular waveguidesknown in microwave engineering are capable of guiding RF power from ahigh-power amplifier 18A-D to the enclosed cavity 20 with a powerattenuation of approximately 0.03 decibels per meter.

Additionally, each of the RF feeds 26A-D can include a sensingcapability to measure the magnitude of the forward and the backwardpower levels or phase at the amplifier output. The measured backwardpower indicates a power level returned to the high-power amplifier 18A-Das a result of an impedance mismatch between the high-power amplifier18A-D and the enclosed cavity 20. Besides providing feedback to thecontroller 14 and the RF signal generator 16 to implement, in part, acooking strategy, the backward power level can indicate excess reflectedpower that can damage the high-power amplifier 18A-D.

Along with the determination of the backward power level at each of thehigh-power amplifiers 18A-D, temperature sensing at the high-poweramplifier 18A-D, including at the dummy load, can provide the datanecessary to determine if the backward power level has exceeded apredetermined threshold. If the threshold is exceeded, any of thecontrolling elements in the RF transmission chain including the powersupply 12, controller 14, the RF signal generator 16, or the high-poweramplifier 18A-D can determine that the high-power amplifier 18A-D can beswitched to a lower power level or completely turned off. For example,each high-power amplifier 18A-D can switch itself off automatically ifthe backward power level or sensed temperature is too high for severalmilliseconds. Alternatively, the power supply 12 can cut the directcurrent power supplied to the high-power amplifier 18A-D.

The enclosed cavity 20 can selectively include subcavities 22A-B byinsertion of an optional divider 24 therein. The enclosed cavity 20 caninclude, on at least one side, a shielded door to allow user access tothe interior of the enclosed cavity 20 for placement and retrieval offood or the optional divider 24.

The transmitted bandwidth of each of the RF feeds 26A-D can includefrequencies ranging from 2.4 GHz to 2.5 GHz. The RF feeds 26A-D can beconfigured to transmit other RF bands. For example, the bandwidth offrequencies between 2.4 GHz and 2.5 GHz is one of several bands thatmake up the industrial, scientific and medical (ISM) radio bands. Thetransmission of other RF bands is contemplated and can includenon-limiting examples contained in the ISM bands defined by thefrequencies: 13.553 MHz to 13.567 MHz, 26.957 MHz to 27.283 MHz, 902 MHzto 928 MHz, 5.725 GHz to 5.875 GHz and 24 GHz to 24.250 GHz.

Referring now to FIG. 2, a block diagram of the RF signal generator 16is shown. The RF signal generator 16 includes a frequency generator 30,a phase generator 34 and an amplitude generator 38 sequentially coupledand all under the direction of an RF controller 32. In this way, theactual frequency, phases and amplitudes to be output from the RF signalgenerator 16 to the high-power amplifiers are programmable through theRF controller 32, preferably implemented as a digital control interface.The RF signal generator 16 can be physically separate from the cookingcontroller 14 or can be physically mounted onto or integrated into thecontroller 14. The RF signal generator 16 is preferably implemented as abespoke integrated circuit.

As shown in FIG. 2 the RF signal generator 16 outputs four RF channels40A-D that share a common but variable frequency (e.g. ranging from 2.4GHz to 2.5 GHz), but are settable in phase and amplitude for each RFchannel 40A-D. The configuration described herein is exemplary andshould not be considered limiting. For example, the RF signal generator16 can be configured to output more or less channels and can include thecapability to output a unique variable frequency for each of thechannels depending upon the implementation.

As previously described, the RF signal generator 16 can derive powerfrom the power supply 12 and input one or more control signals from thecontroller 14. Additional inputs can include the forward and backwardpower levels determined by the high-power amplifiers 18A-D. Based onthese inputs, the RF controller 32 can select a frequency and signal thefrequency generator 30 to output a signal indicative of the selectedfrequency. As represented pictorially in the block representing thefrequency generator 30 in FIG. 2, the selected frequency determines asinusoidal signal whose frequency ranges across a set of discretefrequencies. In one non-limiting example, a selectable bandwidth rangingfrom 2.4 GHz to 2.5 GHz can be discretized at a resolution of 1 MHzallowing for 101 unique frequency selections.

After the frequency generator 30, the signal is divided per outputchannel and directed to the phase generator 34. Each channel can beassigned a distinct phase, that is, the initial angle of a sinusoidalfunction. As represented pictorially in the block representing the perchannel phase generator 36A-D in FIG. 2, the selected phase of the RFsignal for a channel can range across a set of discrete angles. In onenon-limiting example, a selectable phase (wrapped across half a cycle ofoscillation or 180 degrees) can be discretized at a resolution of 10degrees allowing for 19 unique phase selections per channel.

Subsequent to the phase generator 34, the RF signal per channel can bedirected to the amplitude generator 38. The RF controller 32 can assigneach channel (shown in FIG. 2 with a common frequency and distinctphase) to output a distinct amplitude in the channel 40A-D. Asrepresented pictorially in the block representing the per channelamplitude generator in FIG. 2, the selected amplitude of the RF signalcan range across a set of discrete amplitudes (or power levels). In onenon-limiting example, a selectable amplitude can be discretized at aresolution of 0.5 decibels across a range of 0 to 23 decibels allowingfor 47 unique amplitude selections per channel.

The amplitude of each channel 40A-D can be controlled by one of severalmethods depending upon the implementation. For example, control of thesupply voltage of the amplitude generator 38 for each channel can resultin an output amplitude for each channel 40A-D from the RF signalgenerator 16 that is directly proportional to the desired RF signaloutput for the respective high-power amplifier 18A-D. Alternatively, theper channel output can be encoded as a pulse-width modulated signalwhere the amplitude level is encoded by the duty cycle of thepulse-width modulated signal. Yet another alternative is to coordinatethe per channel output of the power supply 12 to vary the supply voltagesupplied to each of the high-power amplifiers 18A-D to control the finalamplitude of the RF signal transmitted to the enclosed cavity 20.

As described above, the electromagnetic cooking device 10 can deliver acontrolled amount of power at multiple RF feeds 26A-D into the enclosedcavity 20. Further, by maintaining control of the amplitude, frequencyand phase of the power delivered from each RF feed 26A-D, theelectromagnetic cooking device 10 can coherently control the powerdelivered into the enclosed cavity 20. Coherent RF sources deliver powerin a controlled manner to exploit the interference properties ofelectromagnetic waves. That is, over a defined area of space andduration of time, coherent RF sources can produce stationaryinterference patterns such that the electric field is distributed in anadditive manner. Consequently, interference patterns can add to createan electromagnetic field distribution that is greater in amplitude thanany of the RF sources (i.e. constructive interference) or less than anyof the RF sources (i.e. destructive interference).

The coordination of the RF sources and characterization of the operatingenvironment (i.e. the enclosed cavity and the contents within) canenable coherent control of the electromagnetic cooking and maximize thecoupling of RF power with an object in the enclosed cavity 20. Efficienttransmission into the operating environment can require calibration ofthe RF generating procedure. As described above, in an electromagneticheating system, the power level can be controlled by many componentsincluding the voltage output from the power supply 12, the gain onstages of variable gain amplifiers including both the high-poweramplifiers 18A-D and the amplitude generator 38, the tuning frequency ofthe frequency generator 30, etc. Other factors that affect the outputpower level include the age of the components, inter-componentinteraction and component temperature.

Referring now to FIG. 3, a schematic diagram illustrating a high-poweramplifier 18 coupled to a waveguide 110 in accordance with variousaspects described herein is shown. The high-power amplifier 18 includesone or more amplification stages 100 coupled via a guiding structure 102to a circulator 104. The circulator 104 is coupled by a guidingstructure 106 to a waveguide exciter 108. The high-power amplifier 18 iselectrically coupled to the waveguide 110 by the waveguide exciter 108and mechanically coupled by an electromagnetic gasket 112.

The high-power amplifier 18 is configured such that a number ofamplification stages 100 are interconnected to amplify a radio frequencysignal from the amplifier input to the amplifier output. Theamplification stages 100 include one or more transistors configured toconvert a small change in input voltage to produce a large change inoutput voltage. Depending upon the configuration of the circuit, theamplification stages 100 can produce a current gain, a voltage gain orboth.

The output of the amplification stages 100 is coupled to the circulator104 via a guiding structure 102. The guiding structure 102 can be anyelectrical connector capable of carrying high-power radio frequencysignal including but not limited to a microstrip printed on a dielectricsubstrate of a printed circuit board. The circulator 104 is a passivemulti-port component that transmits radio frequency signals from oneport to the next where a port is a point on the circulator 104 forcoupling a radio frequency signal from one component to another. In thehigh-power amplifier 18, the circulator 104 acts as a protective deviceto isolate the amplification stages 100 from deleterious effects thatcan occur when a mismatched load reflects power.

The circulator 104 is coupled to the waveguide exciter 108 via theguiding structure 106. The high-power amplifier 18 is terminated at itsoutput by the waveguide exciter 108. The waveguide exciter 108 convertselectromagnetic energy from a first mode suitable for transmissionwithin the high-power amplifier 18 to a second mode suitable fortransmission within the waveguide 110. In this way, the waveguide 110acts as an RF feed 26A-D to convey the amplified electromagnetic signalfrom the high-power amplifier to the microwave cavity.

The electromagnetic gasket 112 provides a secure connection between thehigh-power amplifier 18 and the waveguide 110 and surrounds the portionof the waveguide exciter 108 positioned between the high-power amplifier18 and the waveguide 110. The electromagnetic gasket 112 can be formedof one or more materials useful for securing the connection between thehigh-power amplifier 18 and the waveguide 110 and providingelectromagnetic shielding at radio frequencies. Such materials caninclude, but are not limited to, silicone-based constituents filled withconductive particles such as silver or nickel.

The provision of the waveguide exciter 108 that terminates the output ofthe high-power amplifier 18 reduces the electromagnetic losses typicallyincurred at the junction of microwave devices coupled via conventionalconnectors. That is, conventional microwave devices are interconnectedvia coaxial connectors (e.g. BNC or N-type connectors) that incur RFlosses due to the additional path lengths for the connectors as well asthe losses at the coupling of the coaxial connectors. Theelectromagnetic gasket 112 augments the efficiency of the waveguideexciter 108 by shielding the waveguide exciter 108 as well as providingthe mechanical support of the coupling between the high-power amplifier18 and the waveguide 110.

Referring now to FIG. 4, a cross-sectional side view illustrating thecirculator 104 in accordance with various aspects described herein isshown. As described above, the circulator 104 is coupled to the outputof the amplification stages via the guiding structure 102. Thecirculator 104 includes a laminate 122 mounted to a metal base plate120.

Two ferrite magnets 126, 128 in axial alignment perpendicular to thelaminate 122 are secured to the laminate 122 by clips 130. The ferritemagnets 126, 128 can be any shape suitable for the circulator design,including, but not limited to a disk.

The guiding structure 102 can include a microstrip that is printed on alaminate 122. The laminate 122 is a dielectric substrate that caninclude any material suitable for the provision of insulating layers ofa printed circuit board including, but not limited to, FR-2 material orFR-4 material. The laminate 122 is positioned on the metal base plate120 that provides mechanical support to the circulator 104.Additionally, the metal base plate 120 acts as a thermal dissipatingmass and to spread heat generated by the circulator 104. The metal baseplate 120 includes a pocket 124 to house the lower ferrite magnet 128.

During the manufacturing of the circulator 104, the lower ferrite magnet128 is placed in the pocket 124 of the metal base plate 120. Thelaminate 122 and microstrip guiding structure are applied to the metalbase plate 120. The upper ferrite magnet 126 is placed above lowerferrite magnet 128 and secured to the laminate 122 by clips 130.

FIG. 5 is a top-view diagram illustrating the integrated circulator ofFIG. 4.

As described, the circulator 104 includes, as part of its magneticcircuit, the laminate 122 of a printed circuit board as well as themicrostrip guiding structure 102 coupled to the output of theamplification stages (cf. element 100 in FIG. 3). In this way, thecirculator 104 does not include input or output pins that require asoldered connection during the manufacturing process. Conventionalsolder joints can expose the high-power amplifier to reliability issuesbecause the soldering process can result in cold-spots or bad couplings.Therefore, the circulator 104 is not a conventional discrete componentsoldered in the high-power amplifier. Instead the circulator 104 isdirectly integrated as a component of the high-power amplifier.

For the output power level at the end of the amplification stages 100 tohit a desired set-point level, the RF signal generator (cf. element 16in FIG. 1) can rely on feedback in the form of signals indicative of theforward and backward power levels or the relative phases of the radiofrequency signals conveyed to the enclosed cavity (cf. element 20 inFIG. 1). Therefore, in addition to the amplifying components foroutputting a radio frequency signal that is amplified in power withrespect to an input radio frequency signal, conventional high-poweramplifiers can include a measuring component that outputs a signalindicative of the radio frequency power transmitted and received by theamplifying component. However, by integrating such a measurementcomponent within the high-power amplifier, the output stage of ahigh-power amplifier can incur electrical losses that can reduce thepower and fidelity of the radio frequency signal output to the radiofrequency feed (cf. elements 26A-D in FIG. 1) such as a waveguide.

Referring now to FIG. 6, schematic diagram illustrating a high-poweramplifier 18 coupled to a waveguide 110 with an integrated measurementsystem 150 in accordance with various aspects described herein is shown.The integrated measurement system 150 includes probe antennas 152coupled to electronic components 154. The probe antennas 152 includeportions located within the waveguide 110 that convert radio frequencyelectromagnetic waves within the waveguide 110 into an analog electricpower signal. The probe antennas 152 can be any type of antenna usefulfor measuring radio frequency electromagnetic waves within a waveguide,including but not limited to, dipole antennas.

The electronic components 154 are coupled to the probe antennas 152 andcan include an analog-to-digital convertor (ADC) such that the outputsignal is digital and readily input to a device such as the RF signalgenerator (cf. element 16 in FIG. 1), controller (cf. element 14 inFIG. 1) or the RF controller (cf. element 32 in FIG. 1). The electroniccomponents 154 can be any component useful for the measurement of radiofrequency signals including, but not limited to, radio frequency logpower detectors that provide a direct current output voltage that islog-linear with respect to the detected radio frequency power levelwithin the waveguide 110.

The measurement system can include additional components useful forfurther characterizing the radio frequency transmissions conveyedthrough the waveguide 110. Referring now to FIG. 7, a schematic diagramillustrating a high-power radio frequency amplifier 18 coupled to awaveguide 110 with an integrated measurement system 160 that includes areflectometer 164 in accordance with various aspects described herein isshown. The integrated measurement system 160 includes probe antennas 162coupled to a reflectometer 164. The probe antennas 162 include portionslocated within the waveguide 110 that convert radio frequencyelectromagnetic waves within the waveguide 110 into an analog electricpower signal. The probe antennas 162 can be any type of antenna usefulfor measuring radio frequency electromagnetic waves within a waveguide,including but not limited to, dipole antennas.

The reflectometer 164 can include any components useful for measuringthe phase of a radio frequency signal including, but not limited to, adirectional coupler containing matched calibrated detectors or a pair ofsingle-detector couplers oriented so as to measure the electrical powerflowing in both directions within the waveguide 110. In this way, theintegrated measurement system 160 can characterize the radio frequencytransmissions according to power and phase and can be used to form anetworked description as embodied in the scattering matrix orS-parameters. In one non-limiting implementation, the reflectometer 164is a six port reflectometer configured to measure the phase of theforward and backward radio frequency radiation within the waveguide.

The reflectometer 164 is coupled to the probe antennas 162 and caninclude an analog-to-digital convertor (ADC) such that the output signalindicative of the phase or power of the radio frequency electromagneticwave within the waveguide 110 or scattering matrix is digital andreadily input to a device such as the RF signal generator (cf. element16 in FIG. 1), controller (cf. element 14 in FIG. 1) or the RFcontroller (cf. element 32 in FIG. 1).

By characterizing the conveyed radio frequency transmissions accordingto power and phase measurements or scattering matrix, theelectromagnetic cooking device (cf. element 10 in FIG. 1) withsolid-state radio frequency sources can precisely excite an enclosedcavity (cf. element 20 in FIG. 1) by controlling the coupling factor ofthe resonant modes or standing waves that determine the heating patterntherein. That is, a solid-state electromagnetic cooking device canenergize desired heating patterns by coupling specific resonant modes tothe microwave cavity via the actuation of the radio frequency sourceswhere the heating pattern is determined by the modulus of the resonantmode. The resonant modes are a function of the cavity dimension, foodload type, food load placement and excitation condition of the multiplecoherent radio frequency sources (e.g. the operating frequency and phaseshift between the sources, etc.). The electromagnetic cooking device canbe configured to control the solid-state radio frequency sources toselect the coupling factor of the resonant modes to energize a specificheating pattern or a sequence of heating patterns over time. The heatingpatterns related to specific resonant modes can determine the evennessor unevenness of the cooking process. However, because the resonantmodes are a function of the food load type and placement, the cavitysize and excitation condition, it is not possible to have an a prioriknowledge of the resonant modes and their critical frequencies.

Therefore, the electromagnetic cooking device can be configured todetermine the resonant modes within an enclosed cavity in-situ.Referring now to FIG. 8, a schematic diagram illustrating a resonantcavity 222 coupled to two RF feeds 226A,B embodied as waveguides inaccordance with various aspects described herein is shown. The RF feeds226A,B couple power from their respective high-power amplifiers (cf.elements 18A,B in FIG. 1) to the enclosed cavity 222. The RF feeds226A,B can be coupled to the enclosed cavity 222 in spatially separatedbut fixed physical locations. The RF feeds 226A,B can convey RFtransmissions to the enclosed cavity 222 at a selected frequency andphase where the phase shift or difference between the RF transmissionsdirectly relates to the class of symmetry of the coupled resonant mode.For example activating the RF sources in an in-phase relationship (i.e.phase shift=0°) activates modes of even symmetry while activating thesources in an antiphase relationship (i.e. phase shift=) 180° activatesmodes of odd symmetry. The symmetries determine the heating patterns inthe oven as will be described below.

In operation, the electromagnetic cooking device determines the set ofsymmetries (e.g. even or odd) for the resonant modes to be excitedwithin the cavity 222. The electromagnetic cooking device is configuredto excite the cavity 222 for a set of operating frequencies and storethe efficiency measured for each frequency. The efficiency is determinedby the useful power output divided by the total electrical powerconsumed which can be measured according to the ratio of forward powerless the backward power to forward power as in:

$\eta = \frac{{\sum\; P_{forward}} - {\sum\; P_{backward}}}{\sum\; P_{forward}}$

The electromagnetic cooking device is configured to store the efficiencymap in memory for the excited classes of symmetries.

Referring now to FIG. 9, a graphical diagram illustrating efficiencyversus frequency for in-phase excitations 228 and antiphase excitations230 of the resonant cavity is shown. In this non-limiting illustrativeexample, the electromagnetic cooking device is configured to conduct twosets of excitations for each operating frequency and obtain twoefficiency measurements.

Referring now to FIG. 10, a diagram illustrating features of a method ofanalysis to determine the resonant modes of the cavity in accordancewith various aspects described herein is shown. The electromagneticcooking device can analyze the recorded map of efficiency (shown for thein-phase excitation 228) by modeling the response as a passband RLCcircuit in order to recognize the critical frequencies of the poles(i.e. the resonant frequencies of the resonant modes) that have beenexcited for the specific class of symmetry. For this purpose, aprocessor 250 as a physical or logical subcomponent of the controller(cf. element 14 in FIG. 1) or the RF controller (cf. element 32 inFIG. 1) can be configured to identify local maxima of the efficiencyfunction. The processor 250 can implement any algorithm useful fordetermining the critical frequencies of the poles of the efficiency mapincluding, but not limited to vector fitting, magnitude vector fitting,etc. In this way, the processor 250 can determine a list of resonantfrequencies 252 for each symmetry plane.

Additionally, the processor 250 can determine the quality factor basedon the relative bandwidth of each determined pole. The processor 250 candetermine the presence of foodstuff located within the cavity based onthe estimate of the quality factor. For example, if the processor 250determines that a selected resonant mode has a low quality factor suchas at or below seven, the processor 250 can determine that the portionsof the enclosed cavity where the excited mode has a local or globalmaximum contain foodstuff. Similarly, if the processor 250 determinesthat a selected resonant mode has a high quality factor such as greaterthan 1000, the processor can determine that the portions of the enclosedcavity where the excited mode has a local or global maximum do not havefoodstuff. The processor 250 can classify the type of foodstuff locatedwithin the cavity based on the estimate of the quality factor. Forexample, frozen food has a quality factor of about 300, water has aquality factor of about 7 and metal objects has a quality factor ofabout 1000. For each determined pole, the processor 250 can associate aresonant frequency used to excite the mode and a quality factor fordetermining the type of foodstuff that will be heated by the mode.

Referring now to FIG. 11, a diagram illustrating features of a method tocharacterize the resonant modes of the cavity in accordance with variousaspects described herein is shown. Building on the previously describedexample of an in-phase excitation 228 of the radio frequency feeds226A,B where a processor of the electromagnetic cooking devicedetermines a set of poles 252 indicative of the resonant modes excitablein the cavity 222, the determined poles 252A-C each correspond to aheating pattern 260A-C within the cavity 222. Recall that the heatingpattern is determined by the modulus of the resonant mode. Each heatingpattern 260A-C will have a spatial pattern with contours indicative ofuniform heating. While depicted in FIG. 11 with a binary set ofcontours, the actual heating patterns will include many contoursindicative of a continuum of heating levels. For ease of understanding,the single contour level indicates the hottest areas of the heatingpattern and demonstrate the even and odd symmetries of the resonantmodes.

Referring now to FIG. 12, a schematic diagram illustrating features of amethod to locate and classify foodstuff 300A,B positioned within aresonant cavity 222 in accordance with various aspects described hereinis shown. Initiating an in-phase excitation, the electromagnetic cookingdevice can generate a heating pattern 360A in the cavity 222 with aneven symmetry where the maximum heating contours 302 do not occur in thecenter of the cavity 222. Because a large portion 312 of the foodstuff300A is lying within a minimum of the heating pattern 360A, the cavityreflections are more significant the electromagnetic response from thefoodstuff 300A leading to a relatively low efficiency. In contrast,because a large portion 314 of the foodstuff 300B is lying within amaximum of the heating pattern 360B for an antiphase excitation, thecavity reflections are minimized and the efficiency is higher than theefficiency determined during the even symmetry excitation. Therefore,the electromagnetic cooking device can determine if foodstuff is locatedin the center of the cavity 222 by comparing the efficiencies betweenthe efficiencies between an in-phase excitation and an antiphaseexcitation. To wit, a higher efficiency with in-phase excitationindicates that foodstuff is not located in the center of the cavity anda higher efficiency with an antiphase excitation indicates the foodstuffis located at the center of the cavity. In this way, the electromagneticcooking device can be configured to determine the presence of foodstuffpositioned in the center of the microwave cavity based on the efficiencyof the activated resonant modes of even symmetry or determine thepresence of foodstuff positioned remotely from the center of themicrowave cavity based on the efficiency of the activated resonant modesof odd symmetry.

Additionally, the processor can be configured to further analyze thequality factors according to the efficiency and symmetry of the resonantmodes to detect and locate more than one type of foodstuff in the cavity222. The processor can be configured to average the quality factors fora subset of the identified resonant modes to classify a portion 310, 314of a foodstuff 300A, 300B according to its position within the microwavecavity 222. For example, the processor can average the quality factorsof the even symmetry modes to determine the type of foodstuff located ina portion 310 of the foodstuff 300A that intersects with the maximumheating contours 302 of the even symmetry heating patterns 360A.Similarly, the processor can average the quality factors of the oddsymmetry modes to determine the type of foodstuff located in a portion314 of the foodstuff 300B that intersects with the maximum heatingcontours 304 of the odd symmetry heating patterns 360B.

Referring now to FIG. 13, a flowchart illustrating a method 400 ofidentifying resonant modes and classifying foodstuff positioned within aresonant cavity in accordance with various aspects described herein isshown. The method 400 includes steps to: excite the microwave cavitywith selected phasors; collect forward and reflected power measurementsfor a set of frequencies and phasors; compute efficiency versusfrequency to determine an efficiency spectrum for the selected phasors;identify the resonant modes of the microwave cavity based on thecomputed efficiency spectrum and classify the foodstuff according to theresonant modes and efficiency spectrum.

At step 402, the electromagnetic cooking device excites the microwavecavity with selected phasors for a set of operating frequencies. Theselected set of phasors can include in-phase phasors where the RF feedsconvey radio frequency signals with no phase shift and antiphase phasorswhere the RF feeds convey radio frequency signals with a phase shift of180°.

At step 404, the electromagnetic cooking device by way of an integratedmeasurement system can collect forward and backward power measurementsin the waveguides of the RF feeds. Alternatively or additionally, themeasurement system can be configured to measure phase or characterizethe radio frequency network according to the scattering parameters.

At step 406, the electromagnetic cooking device by way of a processorcan determine the efficiency spectrum for each symmetry of resonantmode. The processor is configured to determine the efficiency for theoperating set of frequencies for each selected phasor. For example, whenthe selected set of phasors include the in-phase and antiphaserelationships, the processor can determine an efficiency spectrum forthe even and odd modes.

At step 408, the electromagnetic cooking device by way of a processorcan identify the resonant modes in the microwave cavity. The processoris configured to model the cavity as a passband RLC circuit anddetermine the center frequency and quality factor for each poleindicative of a resonant mode.

At step 410, the electromagnetic cooking device by way a processor canclassify foodstuff within the cavity. The processor can be configured tocompare the efficiency between the even and odd symmetry modes to locatethe position of foodstuff within the cavity. The processor can befurther configured to determine the composition of the foodstuff basedon the determined quality factor of the modes. Finally, the processorcan be configured to determine the composition and location of portionsof the foodstuff by averaging quality factors for subset of theidentified resonant modes.

As described above, the method includes steps to determine and classifyresonant modes that are activated when the radio frequency sources of anelectromagnetic cooking device couple energy into a microwave cavitybased on readings of forward and backward power or the phase oftravelling waves. The method enables the electromagnetic cooking deviceto determine the resonant modes based on efficiency measurements of theabsorption spectrum for the transmitted frequencies. Further, the methodenable the electromagnetic cooking device to characterize the spatialdistribution of the resulting heating patterns by the determinedresonant modes. Because a resonant mode exists only at a specificdiscrete frequency, the coupling between the radio frequency sources andthe resonant modes is a function of the operating frequency of the radiofrequency sources. Additionally, the coupling of the sources with themodes of a resonant cavity is a function of the source excitation,source placement and the phase relationship between the sources. Themethod enables the electromagnetic cooking device to locate and identifythe composition of foodstuff to be cooked within the cavity.

For purposes of this disclosure, the term “coupled” (in all of itsforms, couple, coupling, coupled, etc.) generally means the joining oftwo components (electrical or mechanical) directly or indirectly to oneanother. Such joining may be stationary in nature or movable in nature.Such joining may be achieved with the two components (electrical ormechanical) and any additional intermediate members being integrallyformed as a single unitary body with one another or with the twocomponents. Such joining may be permanent in nature or may be removableor releasable in nature unless otherwise stated.

It is also important to note that the construction and arrangement ofthe elements of the device as shown in the exemplary embodiments isillustrative only. Although only a few embodiments of the presentinnovations have been described in detail in this disclosure, thoseskilled in the art who review this disclosure will readily appreciatethat many modifications are possible (e.g., variations in sizes,dimensions, structures, shapes and proportions of the various elements,values of parameters, mounting arrangements, use of materials, colors,orientations, etc.) without materially departing from the novelteachings and advantages of the subject matter recited. For example,elements shown as integrally formed may be constructed of multiple partsor elements shown as multiple parts may be integrally formed, theoperation of the interfaces may be reversed or otherwise varied, thelength or width of the structures and/or members or connector or otherelements of the system may be varied, the nature or number of adjustmentpositions provided between the elements may be varied. It should benoted that the elements and/or assemblies of the system may beconstructed from any of a wide variety of materials that providesufficient strength or durability, in any of a wide variety of colors,textures, and combinations. Accordingly, all such modifications areintended to be included within the scope of the present innovations.Other substitutions, modifications, changes, and omissions may be madein the design, operating conditions, and arrangement of the desired andother exemplary embodiments without departing from the spirit of thepresent innovations.

It will be understood that any described processes or steps withindescribed processes may be combined with other disclosed processes orsteps to form structures within the scope of the present device. Theexemplary structures and processes disclosed herein are for illustrativepurposes and are not to be construed as limiting.

It is also to be understood that variations and modifications can bemade on the aforementioned structures and methods without departing fromthe concepts of the present device, and further it is to be understoodthat such concepts are intended to be covered by the following claimsunless these claims by their language expressly state otherwise.

The above description is considered that of the illustrated embodimentsonly. Modifications of the device will occur to those skilled in the artand to those who make or use the device. Therefore, it is understoodthat the embodiments shown in the drawings and described above is merelyfor illustrative purposes and not intended to limit the scope of thedevice, which is defined by the following claims as interpretedaccording to the principles of patent law, including the Doctrine ofEquivalents.

1. An electromagnetic cooking device comprising: an enclosed cavity; aset of radio frequency feeds configured to introduce electromagneticradiation into the enclosed cavity to heat up and prepare food; a set ofhigh-power radio frequency amplifiers coupled to the set of radiofrequency feeds, each high-power amplifier comprising at least oneamplifying stage configured to output a signal that is amplified inpower with respect to an input radio frequency signal; a signalgenerator coupled to the set of high-power radio frequency amplifiersfor generating the input radio frequency signal; and a controllerconfigured to: cause the signal generator and selected ones of the setof high-power amplifiers to output a radio frequency signal of aselected frequency, a selected phase value and a selected power level,wherein the selected frequency is selected from a set of frequencies ina bandwidth of radio frequency electromagnetic waves, the selected phasevalue is selected from a set of phase values of radio frequencyelectromagnetic waves, and the selected power level is selected from aset of power levels; and identify the resonant modes excited within theenclosed cavity.
 2. The electromagnetic cooking device of claim 1,wherein the controller is further configured to classify foodstuffpositioned within the enclosed cavity according to material compositionor location therein.
 3. The electromagnetic cooking device of claim 1,wherein each of the set of radio frequency feeds includes a waveguidecoupled at one end to one of the high-power radio frequency amplifiersand coupled at the other end to the enclosed cavity.
 4. Theelectromagnetic cooking device of claim 3, wherein each of the set ofradio frequency feeds includes a measurement system configured to outputa digital signal indicative of the radio frequency signal conveyedwithin the waveguide.
 5. The electromagnetic cooking device of claim 4,wherein the measurement system includes at least two probe antennaspositioned within each waveguide.
 6. The electromagnetic cooking deviceof claim 4, wherein the measurement system includes a reflectometerconfigured to measure the phase of the forward and backward radiofrequency electromagnetic signals conveyed within each waveguide.
 7. Theelectromagnetic cooking device of claim 1, wherein each of thehigh-power amplifiers includes an integrated circulator furthercomprising: a microstrip positioned on a laminate of a printed circuitboard configured to receive the output of the at least one amplifyingstage; a metal base plate positioned beneath the laminate of the printedcircuit board; a first ferrite magnet positioned within a pocket formedwithin the metal base plate; a second ferrite magnet positioned aboveand aligned with the first ferrite magnet; and one or more clipsconfigured to secure the second magnet above the first ferrite magnet.8. The electromagnetic cooking device of claim 3, wherein each of thehigh-power amplifiers includes a waveguide exciter with a first portionthat terminates the output of the high-power amplifier and a secondportion positioned within the corresponding waveguide and the waveguideexciter is configured to convert electromagnetic energy from a firstmode suitable for transmission within the high-power amplifier to asecond mode suitable for transmission within the waveguide.
 9. Theelectromagnetic cooking device of claim 8, further including anelectromagnetic gasket configured to secure the connection between eachof the high-power amplifiers and the corresponding waveguide andsurround a portion of the waveguide exciter located between thehigh-power amplifier and the corresponding waveguide.
 10. Theelectromagnetic cooking device of claim 1, wherein the selected phasevalue is selected from a set of phasors with an in-phase relationship toactivate resonant modes of even symmetry within the enclosed cavity andfrom a set of phasors with an antiphase relationship to activateresonant modes of odd symmetry within the enclosed cavity.
 11. Theelectromagnetic cooking device of claim 10, wherein the controller isfurther configured to determine the presence of foodstuff positioned inthe center of the enclosed cavity based on at least one of an efficiencyand a quality factor of the activated resonant modes of even symmetry ordetermine the presence of foodstuff positioned remotely from the centerof the enclosed cavity based on at least one of an efficiency and aquality factor of the activated resonant modes of odd symmetry.
 12. Amethod of exciting an enclosed cavity with radio frequency radiation,the method comprising: exciting the enclosed cavity with a selected setof phasors for a set of frequencies; collecting forward and reflectedpower measurements for the selected set of phasors; determining anefficiency spectrum for the selected set of phasors; identifying theresonant modes of the enclosed cavity based on the computed efficiencyspectrum; and classifying foodstuff located within the enclosed cavitybased on the identified resonant modes.
 13. The method of claim 12,wherein the step of classifying the foodstuff includes identifying thecomposition of the foodstuff.
 14. The method of claim 12, wherein thestep of classifying the foodstuff includes determining the position ofthe foodstuff within the cavity.
 15. The method of claim 12, wherein thestep of identifying the resonant modes includes modelling the enclosedcavity as a passband RLC circuit and determining the criticalfrequencies of the resonant modes that have been excited for a specificclass of symmetry.
 16. The method of claim 15, further includingdetermining a quality factor of each identified resonant mode.
 17. Themethod of claim 15, wherein the step of determining the criticalfrequencies includes a step of vector fitting.
 18. The method of claim15, further includes averaging the quality factors for a subset of theidentified resonant modes to classify at least a portion of thefoodstuff according to its position within the enclosed cavity.
 19. Themethod of claim 12, wherein exciting the enclosed cavity includesselecting the set of phasors with an in-phase relationship to activateresonant modes of even symmetry within the enclosed cavity and selectingthe set of phasors with an antiphase relationship to activate resonantmodes of odd symmetry within the enclosed cavity.
 20. The method ofclaim 19, further including determining the presence of foodstuffpositioned in the center of the enclosed cavity based on the efficiencyof the activated resonant modes of even symmetry or determining thepresence of foodstuff positioned remotely from the center of theenclosed cavity based on the efficiency of the activated resonant modesof odd symmetry.